Currently many different wireless technologies exist that allow for communication over extended distances. A primary example of this can be seen in the numerous cellular communication technologies available. Furthermore, many cell phone handsets contain multiple transceivers. These dual-signal transceivers often have a long-range transceiver for entering into a long-range communications link (e.g., between the cell phone handset and a cellular network), and a short-range transceiver for entering into a short-range communications link (e.g., between the cell phone handset and a wireless headset or earpiece).
However, a signal interference problem can arise in these dual-signal type devices. Despite the fact that the two transmission schemes used in these devices are not the same, and may even be designed not to interfere with each other, there remains the possibility that signals transmitted from the device using a first transmission scheme will nevertheless interfere with signals being received at the device using a second transmission scheme. The reason for this is that a transmitter for the first transmission scheme in the dual-signal device may transmit signals that are strong enough in power, and close enough in proximity, to overwhelm a receiver for the second transmission scheme, regardless of signal type.
Therefore, in dual signal devices it has been necessary to take measures to mitigate the interference caused between the two transceivers in the dual-signal device. One way to achieve interference mitigation is to perform frequency filtering on incoming signals for each transceiver, eliminating frequencies not used by the respective transceivers. If the two transceivers operate at significantly different frequencies, this filtering can prevent interference even when one transceiver is transmitting and the other transceiver is receiving. In such a case, the signals transmitted by the transmitting transceiver will not interfere with the operation of the receiving transceiver, since their frequency components will be largely filtered out of the signals received by the receiving transceiver.
However, this interference mitigation method is not practical when the frequencies used by the two transceivers are sufficiently close that filtering will not be effective. For example, some Worldwide Interoperability for Microwave Access (WiMAX) transceivers operate at 2.3 GHz of 2.5 GHGz, while Bluetooth transceivers operate at frequencies of around 2.4 GHz. These frequencies are close enough that they cannot be effectively separated using filtering.
Another way to mitigate interference is to coordinate the transmission and reception operations of the two co-located transceivers so that they never overlap transmission and reception operations. This can be done using some sort of a coordinated time division multiple access (TDMA) operation. In other words, it schedules each transmitter to operate in a specific and separate time slot.
However, this interference mitigation method may not be practical when two synchronous protocols are used, such as WiMAX and Bluetooth protocols that operate in a voice channel. Such synchronous protocols must maintain continuous streams of data, and may not be able to both split up the available transmission time and also maintain their quality of service requirements.
It would therefore be desirable to provide a way for a dual-signal device that uses transceivers with closely related frequencies (such as WiMAX and Bluetooth) to avoid interference between signal transmissions from the two transceivers.